STMicroelectronics Evaluation board for A5970AD EVALA5970AD EVALA5970AD Hoja De Datos

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In 

, the schematic circuit for a standard buck-boost topology is shown. The output 

voltage is:

where the ideal duty cycle D for the buck boost converter is:

The considerations given in 

 for the real duty cycle are still valid here.

 can be used to calculate the maximum output current.

So, as an example, considering the conversion V

IN 

= 12 V to V

OUT 

= -5 V, I

LOAD

 = 0.3 A:

An important thing to take into account is that the ground pin of the device is connected to 
the negative output voltage. Therefore, the device is subjected to a voltage equal to 
V

IN 

- V

O

, which must be lower than 36 V (the maximum operating input voltage).

V

OUT

V

IN

–

D

1 D

–

-------------



=

D

V

–

OUT

V

IN

V

OUT

–

------------------------------

=

D

5

5 12

+

----------------

0.706

=

=

I

SW

I

LOAD

1 D

–

---------------

0.5

1 0.706

–

------------------------

1A

=

=

=

A5970AD